Multichannel signaling system using delay line to obtain time division



Jan. 14, 1947. LAWSON 2,414,265

' MULTICHANNEL SIGNALING SYSTEM USING DELAY LINE TO OBTAIN TIME DIVISIONFiled March 9, 1944 f f -4-1 m--- my UIJL t J'ender A Mixer f 2 L L L LLJ L L L L' L L J L- r Return 1 LLIN GSWaKm Inventor Dams h AWSoNAttorney iatented Jan. 14, 1947 MULTICHANNEL SIGNALING SYSTEM USINGDELAY LINE TO OBTAIN TIME DIVISION Dennis Illingworth Lawson, Cambridge,England, assignor to Pye Limited, Cambridge, England,

a British company Application March 9, 1944, Serial No. 525,784 In GreatBritain January 7, 1943 2 Claims. (Cl. 179-15) The present inventionrelates to multi-channel signaling systems and more particularly toarrangements for transmitting a plurality of electric signalssimultaneously on a single ultrashort wave carrier, for example, oncentimetre waves. The arrangement according to this invention may beused for transmitting telephone, telegraph, facsimile, teleprinter orother kinds of signals and enables any desired number of channels, forexample, a hundred channels, to

be transmitted on the single carrier frequency.

The present invention is based on transmitting the signals in the formof a series of pulses. the pulses corresponding to the diiierentchannels being transmitted successively in time so that a group ofpulses comprising a pulse of each series is transmitted before the nextsucceeding pulse of any series is sent. The receiving station isprovided with means for separating the pulses so that only the series ofpulses corresponding to one channel are passed to the appropriatereproducing device, the pulses corresponding to other channels beingsimilarly separated and directed to their corresponding reproducingdevices. A synchronizing signal is transmitted between each group ofpulses in order to maintain the separating arrangement at the receiverin synchronisrri with the transmitted groups of pulses.

From another aspect the invention consists in transmitting the signalson a common carrier wave in the form of a series of modulated pulses,the transmission of the pulses corresponding to the different channelsbeing displaced in time so that successive pulses of one channel areseparated by a time period within which one pulse of each of the otherchannels is transmitted. The signals of the various channels are thustransmitted sequentially in groups, the pulses of each series of pulsesof one channel being correspondingly positioned in each group. Means areprovided at the receiver for separating out the pulses of each group anddirecting them to the appropriate reproducing device. Preferably betweeneach group of pulses a synchronising signal is transmitted in order tomaintain the separating arrangement at the receiver in synchronism withthe transmitted groups of pulses. This synchronising signal ispreferably of longer duration than the signal pulses so that thesynchronizing pulses can be separated out by virtue of this fact at thereceiver and used for successively actuating the means for separatingthe different channels in the receiver.

A feature of the invention consists in employing an artificial line foreffecting the phase displacement of the pulses at the transmitting sta-.tion by passing a sine wave through the line and tapping ofi voltagesalong the line for effecting the triggering of the pulse transmitters.At the receiving station a similar artificial line may be employedcorrespondingly to trigger separating devices for separating thereceived pulses.

The signal pulses transmitted may be modulated in width or height asknowqn per se, or they may be modulated in phase as described in myconcurrent application Serial No. 516,491, filed December 31, 1943, forimprovements in Pulse modulation signaling systems. Some of the pulsestransmitted may be' modulated by one method and some by another method,or all the pulses may be modulated by the same method,

In order that the invention may be more clearly understood it will befurther explained by reference to an example described below inconjunction with the accompanying drawing in which Fig. 1 is a diagramof the waveform transmitted according to the invention;

Fig. 2 is a schematic diagram of the transmitter;

Fig. 3 shows the prototype section of an artifiicial line employed inthe invention;

Fig. 4 is a schematic diagram of a suitable receiver.

The example'to be described is of a system operating on centimetre wavesand comprising signal channels. The signals of the channels aretransmitted in groups of 100 signal pulses, one for each channel, andeach group of signal pulses is preceded by a synchronising pulse oflonger duration than the signal pulses. The repetition frequency of thepulse groups may, for example, be 6 kc. per second, thus giving arecurrence period of 166 microseconds between successive synchronisingpulses and between successive signal pulses of each channel. As shown inthe waveform diagram of Fig. 1, the synchronising and signal pulses aretransmitted in the form of rectangular pulses which may be produced inknown manner. The groups of signal pulses are indicated at A1, B1, etc.,A1, B2, etc., the pulses A1, A2, etc., comprising the signal of onechannel, the pulses B1, B2, etc. comprising the signal of a secondchannel, and so on. The synchronising pulses S, transmitted for thepurpose of maintaining the receiver in step with the transmitter, aremade of longer duration than the signal pulses so that they can bediscriminated and separated out by virtue of this fact at the receiver,and a time space is provided between each synchronising pulses S and the01- lowing first signal pulse A1, Az, etc., of each group.

An arrangement suitable for generating and transmitting the waveform ofFig. 1 is illustrated diagrammatically in Fig. 2 in which I representsan oscillator generating a sinusoidal wave of the repetition frequencyof the signaling cycle, viz. 6 kc./sec. in the example quoted, which isfed into a. phase delay unit 2 in the form of an artificial lineconstituted by a series of sections having the prototype shown in Fig. 3which comprises a series inductance L and a shunt capacity C. For ahundred channel system the artificial line may comprise 110 sections, 8of which are used for developing the synchronising pulse, 2 of which areleft blank to provide a space between the synchronising pulse and thefirst signal pulse of a group, and the remaining 100 sections are usedfor generating the signal pulses in proper time sequence. Thus the firstsection of the artificial line from the oscillator l is connected to asynchronising pulse generator 3 and the 11th to the 110th sections areconnected respectively to the 100 signal pulse generators of which thefirst two and last two are indicated by 4, 5, B and I. The signal pulsegenerators are modulated with the sound or other intelligence to betransmitted through the various channels and the outputs from thesynchronising pulse generator and the signal pulse generators are fed toa mixer 8 Where they are mixed in sequence to give a complex signalhaving the waveform shown in Fig. 1, which is used to modulate a carrierwave transmitter 9 in known manner. The mixer 8 may employ multi-gridmixing valves of the character disclosed in the concurrent applicationof B. J. Edwards, Serial No. 528,985, filed March 31, 1944, forimprovements in "Electron discharge devices."

With the given recurrence period of 166 micro seconds, and with thegiven artificial line of 110 sections, the delay time per section asshown in Fig. 3 becomes microseconds, or approximately 1.5 microseconds.If L is the inductance and C is the capacity of the section and if theresistance per section is small compared with wL the phase delay 5 persection is given by and since 5 is small The time delay T per section istherefore The characteristic impedance of the line is Z is convenientlychosen so that the line may be readily matched to the master oscillatorI. For example, if Zo=2700 ohms and T=1.5 microseconcls then C 550 pF,L=4 mh. and

L 2mh The artificial line described is not the only type that wouldproduce the requisite phase shifts; for instance, a series resistanceand shunt capacity line could be used, or alternatively a band or 4scribed the generators of the synchronising and signal pulses aretriggered in sequence and at the correct time intervals, thesynchronising pulse being of longer duration than the signal pulse, toproduce cycles of groups of pulses which are transmitted over the commoncarrier wave.

The corresponding receiving station for use with such a transmission isschematicaiy shown in Fig. 4 where It] represents a receiver of knowntype, from the output of which the synchronising pulses are separated byvirtue of their longer duration by means of a separator circuit ll, suchas is already used in television systems, and are used for synchronisinga 6 kc. sine wave generator [2, the output from which is fed through aphase delay unit l3 consisting of an artificial line similar to thatused at the transmitter. The phase-shifted sine wave is picked on fromthe 11th to the th sections of the unit l3 to trigger one hundred gatevalves of which the first two and last two are represented at M, 15, I6and I1, and to each of whnh is also fed the output from the receiver l0,so that each gatevalve allows only the series of signal pulsescorresponding to one channel to pass therethrough and be fed to theappropriate one of the demodulating and reproducing devices 18 to 2|.

The particular embodiments described are given only by way of example,as various other arrangements may be devised for carrying the inventioninto effect. The scope of the invention is therefore to be limited onlyby the appended I claims.

I claim:

1. A multi-channel signaling system having, at the transmitter, asynchronising pulse generator, a plurality of signal pulse generatorsone for each channel, an oscillator for generating a controlling wave,phase-shifting means fed with said wave for producing a series of delaystherein and having a series of outputs associated with said pulsegenerators respectively for triggering said pulse generatorssuccessively so as to produce during each cycle of said wave a group ofsignal pulses together with a synchronising pulse of approximately thesame amplitude as but of longer duration than the signal pulses, saidphase-shifting means comprising an artificial line composed of a seriesof similar delay sections, of which a number of sections in sequence areallotted one to each signal pulse generator so as to produce signalpulses of equal duration from the respective signal generatorssuccessively, and a plurality of sections in sequence are all allottedto the synchronising pulse generator so as to produce a synchronisingpulse of correspondingly longer duration than a signal pulse, means formodulating each signal pulse generator with the signal of the respectivechannel, means to combine the outputs of said synchronising andmodulated signal pulse generators insequence, and means to modulate asingle carrier frequency Withsaid combined output, the system having, ata receiving station, means for separating the pulses of each receivedgroup of pulses into separate series of pulses corresponding to therespective channels, and means for phasing said separating means insynchronism with said' controlling wave at the transmitter under controlof the received synchronising pulses.

2. A multi-channel signaling system having, at the transmitter, asynchronising pulse generator, a plurality of signal pulse generatorsone for each channel, an oscillator for generating a controlling wave,phase-shifting means fed with said wave for producing a series of delaystherein and having a series of outputs associated with said pulsegenerators respectively for triggering said pulse generatorssuccessively so as to produce during each cycle of said wave a group ofsignal pulses together with a synchronising pulse of approximately thesame amplitude as but of longer duration than the signal pulses, saidphase-shifting means comprising an artificial line composed of a seriesof similar delay sections, of which a number of sections in sequence areallotted one to each signal pulse generator so as to produce signalpulses of equal duration from the respective signal generatorssuccessively, and a plurality of sections in sequence are all allottedto the synchronising pulse generator so as to produce a synchronisingpulse of correspondingly longer duration than a signal pulse, means formodulating each signal pulse generator with the signal of the respectivechannel, means to combine the outputs of said synchronising andmodulated signal pulse generators in sequence, and means to modulate asingle carrier frequency with said combined output, the system having,at a receiving station, means comprising a plurality of signalseparating devices, one for each channel, for separating the pulses ofeach received group of pulses into separate series of pulsescorresponding to the respective channels, a wave generator for producinga wave of frequency equal to that of the controlling wave at thetransmitter, means responsive to the longer duration of thesynchronising pulses for separating the synchronising pulses from thereceived transmission, means for applying the synchronising pulses tosaid wave generator for synchronising the output wave thereof with saidcontrolling wave, phase-shifting means in the form of an artificial linewhich is a. duplicate of the said artificial line at the transmitter,those sections of the line at the receiver which correspond to thesections of the line at the transmitter which are allotted to the signalpulse generators being respectively associated with said separatingdevices, means for applying said synchronised wave to each of saidseparating devices through said artificial line at the receiver so as,under the timing influence of said line, to trigger each of saidseparating devices in turn to respond to the signal pulses of thecorresponding channel, and thereby separate the pulses of each receivedgroup of signal pulses into separate series of pulses corresponding tothe respective channels, and means for demodulating the output of eachof said devices.

DENNIS ILLINGWORTH LAWSON.

